Processes and systems for recovering oil from fermentation products

ABSTRACT

Processes and systems for recovering oil from a fermentation product are provided that optimize oil recovery during fermentation. The processes and systems described herein introduce a gas into the fermentation product in order to cause the oil within the fermentation product to separate therefrom, thereby facilitating its subsequent recovery. The processes and systems described herein can maximize the amount of oil that can be recovered during fermentation.

BACKGROUND 1. Field of the Invention

The present invention relates generally to fermentation processes andsystems. More particularly, the present invention relates generally tooil recovery processes and systems for fermentation systems.

2. Description of the Related Art

The production of ethanol for use as a gasoline additive or a straightliquid fuel continues to increase as petroleum costs rise andenvironmental concerns become more pronounced. Ethanol is generallyproduced using conventional fermentation processes that convert thestarch in plant-based feedstocks into ethanol. While ethanol isgenerally the desired product produced during fermentation, there arealso a number of other byproducts produced during fermentation that alsohave commercial value such as, for example, the oil derived from thefermentation feedstocks.

In certain fermentation processes, it can be financially lucrative toseparate the oil from the fermentation product in order to recover thevaluable oil. Generally, the oil is removed from the fermentationproduct after the ethanol has been removed therefrom. This particularfermentation product is commonly referred to as “whole stillage.” Theoil is typically removed from whole stillage by processing the wholestillage in a decanter to separate it into a light phase and a heavyphase, removing the light phase from the decanter, and concentrating thelight phase via evaporation until a desired solids concentration isachieved. This concentrated phase is commonly referred to as condenseddistiller's solubles (“CDS”). The concentrated phase is then subjectedto an oil separation step, which can involve heating, chemicallytreating, and centrifuging the concentrated phase. Generally, theminimum process involves centrifugation. These processes can generallyrecover 0.5 to 0.8 pounds of oil per bushel of grain. Unfortunately, therecovery processes described above are unable to recover a considerableportion of the oil in the fermentation product and, therefore, areunable to maximize the commercial value of the oil found in fermentationproducts.

Thus, there is a need for processes and systems that can maximize therecovery of the oil present in fermentation feedstocks.

SUMMARY

In one or more embodiments, the present invention concerns a method forrecovering an oil from a fermentation product. The method comprises (a)fermenting an oil-containing biomass feedstock to thereby produce afermentation product; (b) introducing a gas into the fermentationproduct to thereby form an oil-poor component and an oil-rich componentcomprising a free oil; and (c) separating the oil-rich component fromthe oil-poor component to thereby form a recovered oil-rich productcomprising the free oil.

In one or more embodiments, the present invention concerns a method forrecovering an oil from whole stillage. The method comprises (a)fermenting a whole stillage to thereby produce a fermentation product;(b) introducing a gas into the fermentation product to thereby form anoil-poor component and an oil-rich component comprising a free oil; and(c) separating the oil-rich component from the oil-poor component tothereby produce a recovered oil.

In one or more embodiments, the present invention concerns a method forrecovering an oil from a fermentation product. The method comprises (a)fermenting an oil-containing biomass feedstock in a fermentation tank tothereby produce a fermentation product; (b) transferring thefermentation product to a secondary tank from the fermentation tank; (c)introducing a gas into the secondary tank to thereby separate thefermentation product into an oil-poor component and oil-rich componentcomprising a free oil; and (d) separating the oil-rich component fromthe oil-poor component to thereby produce a recovered oil.

In one or more embodiments, the present invention concerns a system forrecovering an oil from a fermentation product. The system comprises (a)a fermentation tank configured to ferment an oil-containing biomassfeedstock to thereby produce a fermentation product; (b) a gas injectionsystem configured to introduce a gas into the fermentation tank thatseparates the fermentation product into an oil-poor component andoil-rich component comprising a free oil; and (c) an oil recoveryapparatus configured to separate the oil-rich component from theoil-poor component.

BRIEF DESCRIPTION OF THE FIGURES

Embodiments of the present invention are described herein with referenceto the following drawing figures, wherein:

FIG. 1 is a flow diagram depicting an exemplary primary fermentationprocess utilizing an optional oil recovery step; and

FIG. 2 is a flow diagram depicting an exemplary secondary fermentationprocess using whole stillage that utilizes an oil recovery step.

DETAILED DESCRIPTION

The following detailed description of embodiments of the inventionreferences the accompanying drawings. The embodiments are intended todescribe aspects of the invention in sufficient detail to enable thoseskilled in the art to practice the invention. Other embodiments can beutilized and changes can be made without departing from the scope of theclaims. The following detailed description is, therefore, not to betaken in a limiting sense. The scope of the present invention is definedonly by the appended claims, along with the full scope of equivalents towhich such claims are entitled.

The present invention is generally directed to processes and systems forrecovering oil from a fermentation product. More particularly, thepresent invention is generally directed to processes and systems thatcan maximize the recovery of oil from a fermentation product byintroducing a gas into the fermentation product to separate the productstherein. As described below in further detail, by introducing a gas intothe fermentation product, the oil in the fermentation product can bemore easily separated and recovered, thereby optimizing the oil recoveryrates. As described below, the present invention allows the oil derivedfrom oil-containing feedstocks to be separated at the fermentationstage, which can require less equipment and greatly increase oilrecovery rates compared to prior art processes.

As discussed below, the oil recovery processes described herein can beoptionally utilized in a primary fermentation process and/or a secondaryfermentation process in order to maximize oil recovery.

A primary fermentation process that can optionally utilize a gasinjection system 10 is depicted in FIG. 1. However, it should be notedthat the primary fermentation process depicted in FIG. 1 can bemodified, in whole or part, by other fermentation steps or componentswithout departing from the scope of the present invention. As usedherein, “primary fermentation” refers to a fermentation process thatutilizes a grain as a feedstock. Other fermentation processes aredescribed and illustrated in U.S. Pat. Nos. 6,660,506, 7,527,941,8,288,138, and 8,409,640 and U.S. Patent Application Publication Nos.2004/0023349, 2010/0021980, 2012/0045545, 2012/0244591, and2013/0149764, all of which are incorporated herein by reference in theirentireties.

Turning to FIG. 1, an oil-containing biomass 12 may be delivered to theethanol production facility by any conventional means known in the artsuch as, for example, railcars, trucks, or barges. Generally, theoil-containing biomass comprises a grain such as, for example, barley,rye, wheat, oats, sorghum, milo, canola, corn, buckwheat, or acombination thereof. As shown in FIG. 1, a sufficient supply of thebiomass to facilitate the primary fermentation process may be stored inone or more grain elevators 14.

Ethanol production can begin by milling or otherwise processing thebiomass into a fine powder or flour by a hammer mill or other millingmachine 16. The milled biomass can have an average particle size of atleast about 100, 500, or 750 μm and/or not more than about 10, 5, or 2mm. More particularly, the milled biomass can have an average particlesize in the range of about 100 μm to 10 mm, 500 μm to 5 mm, or 750 μm to2 mm. As used herein, “average particle size” refers to the averagewidth of the milled biomass particles.

The milled biomass can then be mixed with water in one or more slurrytanks 18 to produce an initial biomass feedstock, which may also bereferred to as a “mash.” The initial biomass feedstock can comprise atleast about 15, 25, 35, 40, or 50 and/or not more than about 90, 80, 75,70, or 65 weight percent of solids. More particularly, the initialbiomass feedstock can comprise in the range of about 15 to 90, 25 to 80,35 to 75, 40 to 70, or 50 to 65 weight percent of solids. Additionallyor alternatively, the initial biomass feedstock can comprise at leastabout 10, 15, 20, 25, 30, or 35 and/or not more than about 95, 90, 80,75, 70, or 60 weight percent of starch. More particularly, the initialbiomass feedstock can comprise in the range of about 10 to 95, 15 to 90,20 to 80, 25 to 75, 30 to 70, or 35 to 60 weight percent of starch. Itshould be noted that all weight percentages described herein are basedon total weight of the feedstock unless otherwise noted.

Furthermore, the initial biomass feedstock can comprise a significantamount of water from the slurry tanks 18. For example, the biomassfeedstock can comprise at least about 10, 25, 40, or 50 and/or not morethan about 85, 80, 75, or 65 weight percent of water. More particularly,the biomass feedstock can comprise in the range of about 10 to 85, 25 to80, 40 to 75, or 50 to 65 weight percent of water.

The initial biomass feedstock for the primary fermentation can alsoinclude recycled components from previous fermentation processes, whichcan be added to the feedstock in the slurry tanks 18. For example, theinitial biomass feedstock can comprise a whole stillage and/or thinstillage derived from a previous fermentation process. In one or moreembodiments, the initial biomass feedstock can comprise at least about0.5, 1, or 2 and/or not more than about 20, 10, or 5 weight percent of athin stillage recycled from a previous fermentation process. Moreparticularly, the initial biomass feedstock can comprise in the range ofabout 0.5 to 20, 1 to 10, or 2 to 5 weight percent of a thin stillagederived from a previous fermentation process. Furthermore, in suchembodiments, at least 5, 20, or 40 and/or not more than about 95, 80, or60 percent of the water in the biomass feedstock can be derived from thethin stillage.

As shown in FIG. 1, the initial biomass feedstock can then be mixed withenzymes in a liquefaction tank 20 and held in this tank for a sufficientamount of time to enable the enzymes to begin hydrolyzing the starch inthe feedstock into fermentable sugars. In certain embodiments, theamount of enzyme activity in this step, especially if gluco-amylase isutilized, may be maintained at lower levels in order to leave more longchain sugars in the biomass feedstock. The enzymes can comprise, forexample, a protease, alpha-amylase, gluco-amylase, xylanase,cellobiohydrolase, beta-glucosidase cellulase, amylase, hemicellulase,or combinations thereof. The enzymes may be added at a concentration inthe range of about 0.001 to 0.5, 0.005 to 0.3, or 0.01 to 0.2 weightpercent based on the dry weight of the solids. The temperatures andconditions for this treatment can vary depending on the type of enzymesused. During this treatment, at least 10, 20, or 30 and/or not more than90, 70, or 60 percent of the starch present in the biomass feedstock canbe hydrolyzed into long chain sugars. More particularly, this treatmentcan hydrolyze in the range of 10 to 90, 20 to 70, or 30 to 60 percent ofthe starch into long chain sugars.

Turning again to FIG. 1, the treated biomass feedstock is introducedinto one or more fermentation tanks 22 wherein one or more yeast typesare added to facilitate fermentation. In various embodiments, the addedyeast comprises Saccharomyces cerevisiae. The primary fermentationprocess produces a primary fermentation product that can comprisealcohols, oil, and various other solid and liquid byproducts. Theprimary fermentation product may also be commonly referred to as “beer”by those skilled in the art. The primary fermentation step describedherein can convert at least about 50, 75, 85, or 95 percent of thestarch originally found in the biomass into the primary fermentationproduct.

The primary fermentation can occur over a time period in the range of 12to 150, 24 to 130, or 36 to 110 hours. Furthermore, depending on thetype of yeasts used, the primary fermentation can generally occur at atemperature in the range of 50 to 140, 70 to 120, or 80 to 97° F. Inaddition, the primary fermentation can occur at a pH in the range ofabout 3 to 8, 3.5 to 6, or 4 to 5.

In order to compensate for the possible high viscosity of the feedstockdue to its solids content, a larger amount of alpha-amylase enzymes canbe added to the feedstock before fermentation during the liquefactionstep or during fermentation itself. Consequently, these enzymes canbreak down some of the starch in the feedstock, thereby reducing theviscosity of the biomass feedstock. Thus, the feedstock can be easier tomove throughout the system depicted in FIG. 1. In various embodiments,the alpha-amylase can be derived solely from the grain used as thebiomass feedstock, which have been genetically modified to expresshigher quantities of this enzyme. In such embodiments, additionalalpha-amylase can be added or withheld. In embodiments wherealpha-amylase is added, it may be added at a concentration in the rangeof about 0.001 to 0.5, 0.005 to 0.3, or 0.01 to 0.2 weight percent basedon the dry weight of the solids.

As noted above, the primary fermentation product can comprise multipletypes of alcohols, oil, and other various solid and liquid byproducts.However, ethanol is usually the most important product produced duringthe primary fermentation process. In one or more embodiments, theprimary fermentation product can comprise at least about 7, 10, 13, or15 and/or not more than about 40, 35, 30, or 25 weight percent ofethanol. More particularly, the primary fermentation product cancomprise in the range of about 7 to 40, 10 to 35, 13 to 30, or 15 to 25weight percent of ethanol. Furthermore, the primary fermentation canproduce at least about 1.3, 2.1, 2.25, 2.4, or 2.65 and/or not more thanabout 3.8, 3.5, 3.3, 3.1, or 2.9 gallons of ethanol per bushel of grain.More particularly, the primary fermentation can produce in the range ofabout 1.3 to 3.8, 2.1 to 3.5, 2.25 to 3.3, 2.4 to 3.1, or 2.65 to 2.9gallons of ethanol per bushel of grain.

Other byproducts included in the primary fermentation product caninclude, for example, glycerol, acetic acid, lactic acid, and carbondioxide. In one or more embodiments, the primary fermentation productcan comprise at least about 0.1, 0.5, or 1 and/or not more than about 5,3, or 2 weight percent of glycerol. More particularly, the primaryfermentation product can comprise in the range of about 0.1 to 5, 0.5 to3, or 1 to 2 weight percent of glycerol. Furthermore, the primaryfermentation product can comprise at least about 0.001, 0.005, or 0.01and/or not more than about 0.5, 0.3, or 0.2 weight percent of aceticacid. More particularly, the primary fermentation product can comprisein the range of about 0.001 to 0.5, 0.005 to 0.3, or 0.01 to 0.2 weightpercent of acetic acid. In addition, the primary fermentation productcan comprise at least about 0.001, 0.005, or 0.01 and/or not more thanabout 2, 1.5, or 1 weight percent of lactic acid. More particularly, theprimary fermentation product can comprise in the range of about 0.001 to2, 0.005 to 1.5, or 0.01 to 1 weight percent of lactic acid. It shouldbe noted that the above weight percentages are based on the total weightof the fermentation product unless otherwise noted.

Furthermore, the primary fermentation product can comprise one or moreoils derived from the grain used as the fermentation feedstock. Like theother byproducts in the primary fermentation product, the oils in theprimary fermentation product can also have commercial value. In one ormore embodiments, the primary fermentation product can comprise at leastabout 0.1, 0.5, 1, or 2 and/or not more than 30, 25, 20, or 10 weightpercent of oil derived from the oil-containing biomass feedstock. Moreparticularly, the primary fermentation product can comprise in the rangeof about 0.1 to 30, 0.5 to 25, 1 to 20, or 2 to 10 weight percent of oilderived from the oil-containing biomass feedstock.

Moreover, in various embodiments, at least a portion of the oil in theprimary fermentation product can be “free oil.” As used herein, “freeoil” is oil that is not bound in an emulsion within the fermentationproduct or trapped within a solid portion of the residual oil-containingbiomass in the fermentation product. In one or more embodiments, theprimary fermentation product can comprise at least about 0.1, 0.5, 1, or2 and/or not more than 30, 25, 20, or 10 weight percent of free oil.More particularly, the primary fermentation product can comprise in therange of about 0.1 to 30, 0.5 to 25, 1 to 20, or 2 to 10 weight percentof free oil.

As previously noted, the oil in the primary fermentation product hascommercial value and, thus, it can be desirable to remove this byproductat some point from the fermentation product. Unlike the prior artprocesses, the processes and systems described herein are able toseparate and extract the oil in the fermentation product prior toremoving the ethanol from the fermentation product.

In various embodiments, the free oil in the primary fermentation productcan be brought to the surface of the fermentation product by introducinga gas into the fermentation product. In such embodiments, the introducedgas can cause the oil in the fermentation product to rise to the top ofthe fermentation product, thereby making it easier to recover. The freeoil that agglomerates at the top of the fermentation product can form alayer of free oil that is easily recoverable. In these embodiments, theintroduced gas can form microscopic bubbles that can combine to formlarger bubbles of gas. As these bubbles rise, they can form a convectiveflow of gas through the fermentation product that can bring droplets offree oil to the surface of the fermentation product. During this time,the free oil can become attached or encapsulated within these bubbles,thus allowing the free oil to rise to the top of the fermentationproduct. Thus, introducing a gas into the fermentation product can allowmicroscopic globules of oil to rise and coalesce, thereby creating arecoverable free oil layer.

Thus, in various embodiments, a gas may be introduced into the primaryfermentation product in order to separate the fermentation product intoan oil-poor component and an oil-rich component comprising the free oil.As used herein, “oil-poor” and “oil-rich” refer to the oil content ofthe separated components relative to the oil content of the originalcomponent from which the separated components are derived. Thus, anoil-rich component contains a greater weight percentage of oil than thecomponent from which it is derived, while an oil-poor component containsa lesser weight percentage of oil than the component from which it isderived. In the present case, the oil-rich component contains a higherweight percentage of oil compared to the primary fermentation product,while oil-poor component contains a lower weight percentage of oilcompared to the primary fermentation product.

In one or more embodiments, the gas introduced into the primaryfermentation product can be at least partially derived from, oralternatively, entirely derived from, the gas produced during theprimary fermentation by the yeasts and/or a gas introduced from the gasinjection system 10. The gas can comprise one or many types of gases. Invarious embodiments, the gas comprises carbon dioxide, air, nitrogen, orcombinations thereof. In certain embodiments, the gas comprises carbondioxide.

In various embodiments, the gas can be introduced into the primaryfermentation product through the use of an optional gas injection system10, which can pump a gas stream into the bottom of the fermentation tank22. In one or more embodiments, the gas injection system 10 can beconfigured to pump the gas into the fermentation tank at a sufficientpressure that can overcome the head pressure of the fermentation tank.The gas injection system can comprise any system known in the art thatis capable of injecting a gas into the fermentation tank. For example,the gas injection system can comprise a gas sparger, gas diffuser,aeration turbine, venturi tube, fan, air pump, or a combination thereof.

In various embodiments, the gas introduced into the primary fermentationproduct can be at least partially derived, or alternatively, entirelyderived from the gases produced during fermentation by the yeasts. Asthe yeasts ferment the sugars in the feedstock, various gases can beproduced, such as carbon dioxide.

In certain embodiments, it may be difficult or impose a safety risk toremove oil from the top of an active fermenter. In these cases, it maybe reasonable to process the fermentation product through any number ofadditional steps until it is safe to remove the oil from the top oftank. These additional process steps are discussed below and caninclude, for example, distillation, pressing, and centrifugation. Thetankable liquids left after these processes can then be subjected to gasbubbling by means of the gas injection system 10 in an optional holdingtank 24 as shown in FIG. 1.

The optional holding tank 24 as shown in FIG. 1 can be used to hold thefermentation product after it has been subjected to any number ofpost-fermentation treatment steps, but prior to being separated intooil-poor and oil-rich components as described above. In variousembodiments, the primary fermentation product can be introduced into anoptional holding tank 24. While in the holding tank 24, a gas can beintroduced into the fermentation product, thereby separating thefermentation product into the oil-poor and oil-rich components discussedabove. In such embodiments, the gas can be introduced into the holdingtank 24 from the gas injection system 10. It should be noted that thegas introduced into the holding tank 24 will generally come from the gasinjection system 10 since most of the fermentation will be finished bythis point. An advantage of the gas injection system is that the primaryfermentation product can be separated in non-fermentation tanks

During the gas introduction steps, the gas can be introduced into thefermentation product while in the fermentation tanks and/or holding tankat a sufficient rate so as to cause the fermentation product to separateinto the oil-poor and oil-rich components. In various embodiments, thegas can be introduced into the fermentation product at a rate of atleast about 1, 5, 10, 15, 20, 25, 30, 35, 40, or 45 cm³/min and/or notmore than about 1,000, 750, 500, 400, 350, 300, 250, 200, 150, or 100cm³/min. More particularly, the gas can be introduced into thefermentation product at a rate in the range of about 1 to 1,000, 5 to750, 10 to 500, 15 to 400, 20 to 350, 25 to 300, 30 to 250, 35 to 200,40 to 150, or 45 to 100 cm³/min. Furthermore, the gas can be introducedinto the fermentation product over a time period of at least 0.1, 0.5,1, 2, or 3 hours and/or not more than 24, 12, 10, 8 or 6 hours. Moreparticularly, the gas can be introduced into the fermentation productover a time period in the range of 0.1 to 24 hours, 0.5 to 12 hours, 1to 10 hours, 2 to 8 hours, or 3 to 6 hours.

An analysis of oil recovery through gravity separation in a stagnantfermentation medium with a viscosity of 100 centipoise showed that aspherical oil droplet of 1 mm in diameter will take several days to riseone meter without the aid of gas bubbling. These observations indicatedthat gas bubbling can be necessary to produce a recoverable layer offree-oil in a reasonable time frame.

Furthermore, it has been observed that agitation rates within thefermentation tanks 22 and/or holding tank 24 can affect the separationof the primary fermentation product into the oil-poor and oil-richcomponents during the gas introduction steps. By holding agitation ratesto a low level, at least a portion of the free oil was able to float tothe top of the fermentation product. In such cases, as long as theagitation rates were not high enough to cause a downward velocity thatovercomes the buoyancy of the oil, the free oil can continue to floatand be recovered. If the fermentation product is subjected to excessiveagitation, then the free oil can be redistributed within thefermentation product as bound oil. As used herein, “bound oil” is oil inan emulsion or trapped within the solid portions of the residual biomassfeedstock.

In many embodiments, the fermentation tanks 22 can have an agitator foragitating the fermentation product during fermentation. These agitatorscan include, for example, a mechanical agitator, mechanical stirrer,liquid recirculator, liquid pump, liquid injector, or gas pump. As oneskilled in the art would appreciate, the agitation rate will varydepending on the size of the tank used for fermentation. For example, alaboratory scale bioreactor can utilize an agitator speed in the rangeof 300 to 900 revolutions per minute (“RPM”) during fermentation,whereas a commercial tank capable of holding 100,000 to 1,000,000 literscan utilize an agitator speed in the range of 1 to 50 RPM. Thus, invarious embodiments, the agitation rate of the agitator in thefermentation tank can be closely regulated during the gas introductionstep so as to not interfere with the separation of the fermentationproduct into the oil-poor and oil-rich components. For example, theagitation rate of the agitator during the gas introduction step can beless than 100, 50, 20, 5, or 1 RPM. Furthermore, in embodiments wherethe gas introduction step occurs in the fermentation tank, the agitationspeed of the agitator during the gas introduction can be at least 50,75, 90, or 99 percent less than the agitation speed of the agitatorduring fermentation prior to the gas being introduced.

In various embodiments, the fermentation product is subjected tosubstantially no agitation or no agitation during the gas introductionstep. As used herein, “substantially no agitation” refers to embodimentswhere agitation is not purposely applied such as, for example, throughthe use of an agitator, but does include incidental agitation that maybe the consequence of the environment surrounding the tank.

It should be noted that the gas introduction step can occur duringfermentation or after fermentation when the yeasts have finishedconverting the sugars into the various fermentation products. As notedabove, the gas introduction step, and the subsequent removal of theoil-rich component, can occur in the fermentation tanks 22 or holdingtank 24.

Turning back to FIG. 1, after separating the primary fermentation intothe oil-poor and oil-rich components in the fermentation tanks 22 and/oroptional holding tank 24, the oil-rich component can be recovered fromthe fermentation tanks 22 and/or the holding tank 24 using an oilrecovery system 26. The oil recovery system can comprise any system ormeans known in the art that are capable of removing the top oil-richcomponent from the tanks such as, for example, a pumping apparatus orindustrial pipette. For example, the oil recovery system could comprisea pipe and pump connected to the tank that could remove the top layercomprising the oil-rich component. In such embodiments, the pipe andpump could also remove the top 1% of the fermentation product to ensurethat most, if not all, of the free oil is recovered from thefermentation tank.

The recovered oil-rich component removed by the oil recovery system 26can contain the majority of the free oil originally found in thefermentation product. For example, the recovered oil-rich component cancomprise at least about 25, 50, 75, 90, 95, or 99 percent of the freeoil originally present in the fermentation product. Furthermore, therecovered oil-rich component can comprise at least about 25, 50, 75, 85,90, 95, or 99 weight percent of oil. Moreover, the recovered oil-richcomponent may comprise an oil content by weight percentage that is atleast 25, 50, 75, or 90 percent greater than the oil content by weightpercentage of the primary fermentation product.

In addition to its high oil content, the recovered oil-rich componentmay also comprise some incidental fermentation byproducts. Theseincidental fermentation byproducts can include any of the other productsproduced during fermentation such as, for example, ethanol, glycerol,acetic acid, lactic acid, and unconverted biomass feedstock. Generally,the recovered oil-rich component can comprise less than about 20, 10, 5,1, or 0.1 weight percent of incidental fermentation byproducts.Moreover, the recovered oil-rich component can comprise less than about20, 10, 5, 1, or 0.1 weight percent of water.

In various embodiments, it may be desirable to further treat therecovered oil-rich component in an oil purification system 28 as shownin FIG. 1 in order to concentrate the oil and remove the undesirablebyproducts therein. The oil purification system can comprise any systemknown in the art that is capable of purifying oil such as, for example,a filter membrane, a centrifuge, a settling tank, or a combinationthereof. In one or more embodiments, the oil-rich component can betransferred to a settling tank in order to separate the residualfermentation product from the free oil. While in the settling tank, theheavier residual fermentation product should sink to the bottom. Theheavier residual fermentation product can then be recycled back to thefermentation tank 22 for further conversion or sent to the distillationcolumn 30 for further processing. Additionally or alternatively, therecovered oil-rich component can be processed in a centrifuge in orderto separate the residual fermentation product and the free oil.Furthermore, the oil purification system can utilize one or moresurfactants to facilitate the separation of the incidental fermentationproducts and the free oil.

The purified oil from the oil purification system 28 can comprise atleast about 50, 85, 95, 99, or 99.9 weight percent of oil that wasderived from the oil-containing biomass feedstock used in thefermentation process. Furthermore, the purified oil can comprise lessthan about 5, 3, 1, 0.1, or 0.01 weight percent of water. Moreover, thepurified oil can comprise less than about 10, 5, 3, 1, or 0.1 weightpercent of incidental fermentation byproducts.

In various embodiments, the primary fermentation can produce at leastabout 0.25, 0.5, 0.75, or 1 and/or not more than about 4, 3, 2.5, or 2pounds of recovered oil per bushel of grain. More particularly, theprimary fermentation can produce in the range of about 0.25 to 4, 0.5 to3, 0.75 to 2.5, or 1 to 2 pounds of recovered oil per bushel of grain.Similarly, the primary fermentation can produce at least about 0.1, 0.2,0.3, or 0.4 and/or not more than about 5, 4, 3, or 1 liters of recoveredoil per bushel of grain. More particularly, the primary fermentation canproduce in the range of about 0.1 to 5, 0.2 to 4, 0.3 to 3, or 0.4 to 1liters of recovered oil per bushel of grain.

As noted above, the incidental fermentation product removed by the oilpurification system 28 can be recycled back to the fermentation tank 22for further conversion and/or sent to the distillation column 30 forfurther processing.

As shown in FIG. 1, after recovering the oil-rich component, theoil-poor component remains in the fermentation tank 22 and/or holdingtank 24. The remaining oil-poor component generally comprises thenon-oil byproducts produced during fermentation. For example, theoil-poor component generally comprises ethanol, glycerol, acetic acid,lactic acid, unconverted biomass feedstock, and otherfermentation-derived alcohols. In one or more embodiments, the oil-poorcomponent can comprise at least about 10, 15, 20, or 25 and/or not morethan about 70, 60, 50, or 40 weight percent of ethanol. Moreparticularly, the oil-poor component can comprise in the range of about10 to 70, 15 to 60, 20 to 50, or 25 to 40 weight percent of ethanol.Furthermore, the oil-poor component comprises less than 20, 10, 5, or 1weight percent of oil. Additionally or alternatively, the oil-poorcomponent can comprise an oil content by weight percentage that is atleast 25, 50, 75, or 90 percent lower than the oil content by weightpercentage of the primary fermentation product. In embodiments where aholding tank 24 is utilized, the remaining oil-poor component in theholding tank 24 can be sent to the fermentation tanks 22 for furtherfermentation if necessary.

Turning again to FIG. 1, the remaining oil-poor component or primaryfermentation product (for embodiments where the oil has not been removedduring fermentation) in the fermentation tanks 22 or holding tank 24 canbe transferred to one or more distillation columns 30, which are alsoknown in the art as “beer strippers,” in order to separate the alcohols,especially ethanol, from the solids and other liquids. The alcohol exitsthe top of these columns 30 and can be transferred to one or morerectifiers 32 to further remove moisture from the alcohol. The alcoholmay also be passed to one or more molecular sieves 34 in order to removeeven more moisture. The final alcohol can then be transferred to one ormore ethanol holding tanks 36 where it may be denatured before use as afuel or fuel additive.

The liquid and solid mixture that remains in the distillation columns 30after the alcohol has been removed is commonly referred to as “wholestillage” or simply “stillage.” The mixture can also be commonlyreferred to as “distiller's grains” or “spent distiller's grains.” Thewhole stillage generally settles to the bottom of the distillationcolumns 30 and can then be transferred to one or more whole stillageholding tanks 38.

The whole stillage can comprise at least about 10, 12, 20, or 25 and/ornot more than about 60, 55, 50, or 45 weight percent of solids. Moreparticularly, the whole stillage can comprise in the range of about 10to 60, 12 to 55, 20 to 50, or 25 to 45 weight percent solids.Additionally or alternatively, the whole stillage can comprise at leastabout 5, 15, 25, or 40 and/or not more than about 90, 70, 60, or 50weight percent of water. More particularly, the whole stillage cancomprise in the range of about 5 to 90, 15 to 70, 25 to 60, or 40 to 50weight percent of water.

Although not shown in FIG. 1, the whole stillage produced by the primaryfermentation step can have a number of uses. For example, the wholestillage may be optionally passed through one or more centrifuges, whichcan separate it into a stream of thin stillage and a stream of wetdistiller's grain. Some or all of the thin stillage may be transferredto one or more evaporators to produce an evaporated thin stillage, whichis commonly referred to as “syrup.” The syrup may be used as an animalfeed additive. Furthermore, the wet distiller's grain may be dried toproduce a dried distiller's grain, which may also be utilized as alivestock feed.

Unlike conventional fermentation processes, the processes and systemsdescribed herein do not discard the whole stillage, but can use thisbyproduct to produce additional ethanol and oil. In various embodiments,the whole stillage produced during the primary fermentation can besubjected to a secondary fermentation step in order to maximize oil andethanol production. One advantage of employing the secondaryfermentation described herein is that it can be utilized to maximize oiland ethanol production from the byproducts derived from the primaryfermentation step rather than just using the byproducts as animal feed.

Moreover, in certain embodiments, the secondary fermentation can be usedto release the oil trapped in the various fiber components of the wholestillage. It has been observed that processing of the cellulosic portionduring the secondary fermentation can allow the oil trapped within thefibers of the whole stillage to be released in much greater quantitiescompared to conventional processes. During this process, the fiber inboth the pericarp and the germ, which are oil rich portions of thegrain, can be broken down. As described below, this can be accomplishedthrough a combination of thermal, chemical, mechanical, and enzymaticmeans. As the fiber is broken down, the bound oil can be released fromthe fiber matrix. At the same time, simple sugars are being produced andfermented.

Since whole stillage is generally the byproduct of the fermentation ofcorn or other cereal grain, it can contain a sizable fraction of fiber.All fiber is made up of hemicellulose, cellulose, and lignin. Celluloseconsists of glucose molecules, the same as in starch, but the linkagesin cellulose make it more difficult to break down into individualglucose molecules than in starch. Hemicellulose contains a mixture ofsugars and is generally easier to breakdown than cellulose. Ligninand/or pectin functions as a binder and cannot generally be broken downinto fermentable sugars. The processes of the present invention can alsoinclude steps for converting both the hemicellulose and celluloseportions of the whole stillage into sugars that may be fermented intoethanol.

Prior to the secondary fermentation, the whole stillage can be subjectedto (1) prolonged soaking in the liquefaction tanks, (2) heating in thedistillation columns, and/or (3) chemical reactions from the variouschemical additives added during the primary fermentation. Consequently,these previous steps can help facilitate the breakdown of the fibers inthe whole stillage and make them more inclined to release the oil withinthe fibers during the secondary fermentation.

The secondary fermentation process is depicted in FIG. 2. It should benoted that the secondary fermentation process depicted in FIG. 2 can bemodified, in whole or part, by other fermentation steps or componentswithout departing from the scope of the present invention. As usedherein, “secondary fermentation” refers to a fermentation process thatutilizes a whole stillage as a feedstock. It should be noted that thiswhole stillage can include the whole stillage produced in the primaryfermentation described above or, alternatively, it can include a wholestillage from a different fermentation process in which oil has not beenpreviously removed therefrom.

Prior to the fermentation step, the whole stillage 38 can optionally besubjected to one or more pretreatments in a pretreatment system 40. Thepretreatments can include, for example, steam explosion, acidhydrolysis, alkaline treatment, torrefaction, drying, grinding, soaking,or combinations thereof. The grinding can include, for example, wetmilling or dry milling. These pretreatments can be utilized to breakdown some of the starch, cellulose and/or hemicellulose within the wholestillage into fermentable sugars. In certain embodiments, pretreatingthe cellulose and hemicellulose portions can make these components moreprone to release the bound oils. Thus, this can allow for a greateryield of oil from the fiber components.

In various embodiments, the pretreatment can comprise adding an acid tothe whole stillage to decrease its pH level; heating and pressurizingthe whole stillage; holding the whole stillage under pressure and heat;removing pressure from the whole stillage to cause flashing; and coolingthe whole stillage before the enzymes are added.

Additional pretreatment processes are further described in U.S. PatentApplication Publication Nos. 2012/0045545, 2013/0149763, and2013/0149750, the disclosures of which are incorporated herein byreference in their entireties.

The pretreatments can be used to break down at least a portion of thestarch, cellulose, and/or hemicellulose in the whole stillage intofermentable sugars and can also release the bound oil within the fibers.

Turning again to FIG. 2, after being subjected to the optionalpretreatment in the pretreatment system 40, the pretreated wholestillage can be optionally subjected to enzymatic hydrolysis in anenzymatic hydrolysis system 42. The enzymatic hydrolysis step can beused to break down at least a portion of the starch in the wholestillage into fermentable sugars and can further release some of thebound oil in the fibers of the whole stillage.

It should be noted that the enzymatic hydrolysis during the secondfermentation can be more efficient compared to the hydrolysis step inthe primary fermentation at breaking down the starch into fermentablesugars and releasing the bound oil from the fibrous matrix. This can beattributed to, at least partly, the lower starch concentrations found inthe whole stillage compared to those in the initial biomass feedstockused in the primary fermentation and the greater exposure of the fibrousmatrix in the whole stillage compared to the initial biomass feedstockin the primary fermentation.

Additionally or alternatively, the enzymatic hydrolysis can convert thecellulose portions of the fiber to fermentable sugars and also convertsome of the hemicellulose to sugars. Hexose sugars, such as glucose, maybe produced from the cellulose by the enzymatic hydrolysis. Pentosesugars, such as xylose, may be produced from the hemicellulose duringthe enzymatic hydrolysis.

During enzymatic hydrolysis, one or more enzymes can be added to thewhole stillage to facilitate hydrolyzation of the starch and/or fibersin the whole stillage. In addition, various pH additives can be addedsuch as, for example, ammonia, in order to create an ideal pHenvironment for the added enzymes. Different enzymes may be used tohydrolyze the starch, hemicellulose, and cellulose portions of the wholestillage. The enzymes can comprise, for example, a protease, xylanase,cellobiohydrolase, beta-glucosidase cellulase, amylase, hemicellulase,or combinations thereof. The enzymes may be added at a concentration inthe range of about 0.001 to 0.5, 0.005 to 0.3, or 0.01 to 0.2 weightpercent based on the dry weight of the solids.

As would be readily appreciated in the art, the specific or optimumconditions for enzymatic hydrolysis depend upon the particular enzymesused and are generally optimized to avoid denaturing the enzymes. Forexample, the enzymatic hydrolysis can occur at temperatures in the rangeof 100 to 250° F., 125 to 200° F., or 150 to 160° F. Additionally, theenzymatic hydrolysis can occur at pH in the range of about 2 to 8, 3 to7, or 4 to 6. In various embodiments, the enzymatic hydrolysis for thesecond fermentation can occur at higher temperatures compared to theenzymatic hydrolysis step for the primary fermentation step.

The whole stillage, if subjected to a pretreatment, can be cooled priorto the hydrolysis treatment to a temperature that is more appropriate tofacilitate the hydrolysis. The importance of the enzymatic hydrolysisstep can depend on the severity of the pretreatment process. The lesssevere the pretreatment process, the more important the enzymatichydrolysis can be.

Hemicellulose can be broken down with enzymes that are currentlycommercially available. Hemicellulases are generally used to hydrolyzehemicellulose and contain several different enzymes that hydrolyzespecific bonds in hemicellulose. Hemicellulases are generally mosteffective at temperatures in the range of 155° F. to 185° F., withreduced activity at fermentation temperatures of 90° F. to 95° F. Sincehemicellulose composition varies by feedstock, a hemicellulase that ismost effective for the particular feedstock must be selected inembodiments where hydrolysis of the hemicellulose is desired.

If no fermentation of hemicellulose is being conducted, then theenzymatic hydrolysis step may not be required for fermentation. But thequality of the feed products, the ability to dry the feed, the viscosityof the stillage, and yield of oil can be greatly influenced by thehydrolysis of the hemicellulose. Due to its hydrophilic nature, thehemicellulose tends to bind liquids, especially water. The held watercan increase viscosity, thereby increasing pumping requirements, and canincrease the energy required to dry the final feed product. Oil can alsobecome bound with the hemicellulose, which decreases oil yields. Inaddition, hemicellulose may be more digestable by monogastrics whenhydrolyzed.

Cellulases are the enzymes that can be used to breakdown cellulose intoits derivative sugars and can release the bound oil within the cellulosematrices. However, cellulose can be more difficult to convert to sugarsduring enzymatic hydrolysis because of its crystalline structure. Theglucose is linked to form chains, with crosslinking between the chains.This crosslinking creates much of the difficulty in hydrolyzingcellulose; in effect, it can create a crystalline structure with arelatively small surface area to volume ratio.

Generally, the most effective way of hydrolyzing cellulose is topretreat it prior to enzymatic hydrolysis as described above in order torupture the fiber structure, which creates more surface area anddecrystallizes the cellulose. Non-pretreated cellulose can have astructure with a very small surface area to volume ratio. This limitsthe number of areas available for enzymes to attach and liberate glucosefrom the structure. This determines the effective upper limit forcellulase dosing, thereby limiting the hydrolysis rate. By pretreatingthe cellulose, the crystalline structure can be disrupted and more areasfor attack can be created. The hydrolysis rate is increased bydecreasing polymerization of the cellulose and can be further increasedby increased cellulase dosing.

The enzymatic hydrolysis of the pretreated cellulose can usually beaccomplished in three steps. The first step involves cleaving the longchains of glucose from the cellulose using a whole cellulase, whichrandomly hydrolyzes links in the cellulose. Since this action is random,it can create anything from a single glucose unit to a chain that is afew thousand glucose units long. This is generally the cheapest portionof a cellulase formulation, but since it is random it does not producefree glucose units at a reliable rate. It does, however, create morechains for the next enzymes to act upon. The second step for hydrolyzingpretreated cellulose can be carried out by cellobiohydrolase. Thisenzyme can hydrolyze two units of glucose, termed cellobiose, from theend of a cellulose chain. Since this is not a random attack, the rate ofproduction of cellobiose is predictable. The third step for hydrolyzingpretreated cellulose can be carried out by beta-glucosidase. This enzymecan act on the end of a cellulose chain and hydrolyze single units ofglucose. The chain can be of any length from two units to thousands ofunits long. Generally, the best way to cost effectively hydrolyzecellulose is to balance the use of each one of these enzymes.

Depending on the nature of the enzyme used, the enzymatic hydrolysis caneither be carried out during the subsequent fermentation step describedbelow or as a separate step as described above in a separate tank wherethe temperature can be held higher so as to facilitate the activitylevel of the enzymes. The choice of a separate step or a simultaneousenzymatic and fermentation step depends on the activity of the enzymesused and on viscosity requirements. The whole stillage can become veryviscous during the pretreatment steps, especially when cooled tofermentation temperature. It may be necessary, in some embodiments, tocool the whole stillage to an intermediate temperature where theviscosity is lower and then conduct enzymatic hydrolysis. The wholestillage can then be cooled to fermentation temperatures withoutexcessive viscosity issues.

In various embodiments, the hydrolysis rates can determine the timenecessary for the fermentation step. By increasing the rate ofhydrolysis, the required fermentation time can be reduced. This can beattractive if a fermentation organism is capable of metabolizing theproduced sugar as quickly as it is being liberated. The reducedfermentation time reduces the fermentation capacity required, therebyreducing capital costs.

Turning yet again to FIG. 2, after being subjected to the optionalenzymatic hydrolysis in the system 42, the whole stillage can besubjected to a secondary fermentation in one or more fermentation tanks44 to produce a secondary fermentation product. The yeast utilized inthe secondary fermentation can include one or more types of yeasts andcan depend on the sugar available for fermentation. For example,Saccharomyces cerevisiae is generally only able to ferment hexose sugarsand, therefore, cannot generally use the pentose sugars unlocked fromthe hemicelluloses. Thus, in such embodiments, two outcomes cangenerally occur. Either an infectious organism begins to consume thepentose sugars and some of the hexose sugars, or no infection occurs andthe pentose sugars remain in solution. In the first case, the finalneutral detergent fiber content of the whole stillage produced by thesecondary fermentation can be reduced and protein content can beincreased, with a slight change in amino acid profile. In the secondcase, the neutral detergent fiber levels of the whole stillage producedby the secondary fermentation can remain higher, but can exhibit areduction in the percentage of protein.

Due to the diversity of sugars that can be found in the whole stillage,different combinations of yeasts may need to be utilized in thesecondary fermentation to maximize sugar conversion. In one or moreembodiments, the yeasts are selected from the group consisting ofSaccharomyces cerevisiae, Pichia stipitis, Candida shehatae, andcombinations thereof. In certain embodiments, the yeast utilized in thesecondary fermentation can be the same or different from the yeastutilized in the primary fermentation step. In one embodiment, the yeastis Saccharomyces cerevisiae.

In various embodiments, the secondary fermentation can occur in the samesystem and/or vessel as the primary fermentation. Alternatively, thesecondary fermentation can occur in a separate system and/or vessel thanthe primary fermentation.

The conditions of the secondary fermentation can vary depending on thesugars present in the feedstock and the effects of the previouspretreatment and hydrolysis steps (if utilized). For example, thesecondary fermentation can occur over a time period in the range of 12to 150, 24 to 130, or 36 to 110 hours. Generally, at least 20 hours offermentation time is necessary to ferment about 80 percent of the sugarsin the whole stillage; however, longer time periods can be necessary inorder to ferment the sugars that can be found in hemicellulose andcellulose. Fermentation usually ceases when the feedstock for the yeastsbecomes exhausted. If fermentation is extended beyond this point, thenthe yeast can go through autolysis and begin to consume their ownstructural carbohydrates. This can increase the protein levels of thewhole stillage byproduct but can have very little influence on finalethanol yields.

Furthermore, depending on the type of yeasts used, secondaryfermentation can occur at a temperature in the range of 50 to 140, 70 to120, or 80 to 97° F. In addition, the secondary fermentation can occurat a pH in the range of about 3 to 8, 3.5 to 6, or 4 to 5.

During the first 4 to 6 hours of the fermentation, little to no ethanolcan be produced since it is generally during this phase that the yeastare reproducing. In certain embodiments, the starch is the mostaccessible sugar during these early stages and, therefore, theproduction of the yeast cells can be generally fueled by the starch.During the post-reproduction phase of fermentation, the yeast can beginto produce ethanol. This can occur as glucose is slowly liberated fromthe cellulose chains.

Like the primary fermentation product, the secondary fermentationproduct can comprise multiple types of alcohols and other various solidand liquid byproducts. However, ethanol is usually the most importantproduct produced during the secondary fermentation process. In one ormore embodiments, the secondary fermentation product can comprise atleast about 1, 2, 3, or 3.5 and/or not more than about 25, 20, 15, or 10weight percent of ethanol. More particularly, the secondary fermentationproduct can comprise in the range of about 1 to 25, 2 to 20, 3 to 15, or3.5 to 10 weight percent of ethanol.

Furthermore, due to the lower starch concentrations of the wholestillage, the ethanol concentration produced during the secondaryfermentation can also be low, thereby allowing the yeast to have longeraccess to the sugars in the whole stillage. Consequently, in variousembodiments, this can lead to higher yields of ethanol per bushel ofgrain. For example, the secondary fermentation can produce at leastabout 0.15, 0.3, 0.35, or 0.4 and/or not more than about 1.5, 1.0, 0.8,or 0.6 gallons of ethanol per bushel of grain. More particularly, thesecondary fermentation can produce in the range of about 0.15 to 1.5,0.3 to 1.0, 0.35 to 0.8, or 0.4 to 0.6 gallons of ethanol per bushel ofgrain. Furthermore, the secondary fermentation can convert at least 75,80, 85, or 90 percent of the starch in the whole stillage into thesecondary fermentation product.

In various embodiments, the secondary fermentation can convert at leasta portion of the cellulose and/or hemicellulose in the whole stillageinto fermentation products. For example, the secondary fermentation canconvert at least about 30, 40, 50, 60, or 70 percent of the celluloseoriginally found in the whole stillage into the secondary fermentationproduct. Additionally or alternatively, the secondary fermentation canconvert at least about 30, 40, 50, 60, or 70 percent of thehemicellulose originally found in the whole stillage into the secondaryfermentation product.

Other byproducts included in the secondary fermentation product caninclude, for example, glycerol, acetic acid, lactic acid, and carbondioxide. In one or more embodiments, the secondary fermentation productcan comprise at least about 0.001, 0.005, or 0.01 and/or not more thanabout 1.5, 0.5, or 0.1 weight percent of glycerol. More particularly,the secondary fermentation product can comprise in the range of about0.001 to 1.5, 0.005 to 0.5, or 0.01 to 0.1 weight percent of glycerol.Furthermore, the secondary fermentation product can comprise at leastabout 0.0001, 0.001, or 0.01 and/or not more than about 0.5, 0.3, or 0.2weight percent of acetic acid. More particularly, the secondaryfermentation product can comprise in the range of about 0.0001 to 0.5,0.001 to 0.3, or 0.01 to 0.2 weight percent of acetic acid. In addition,the secondary fermentation product can comprise at least about 0.001,0.005, or 0.01 and/or not more than about 2, 1.5, or 1 weight percent oflactic acid. More particularly, the secondary fermentation product cancomprise in the range of about 0.001 to 2, 0.005 to 1.5, or 0.01 to 1weight percent of lactic acid. It should be noted that the above weightpercentages are based on the total weight of the fermentation productunless otherwise noted.

Furthermore, the secondary fermentation product can comprise one or moreoils derived from the hemicellulose, cellulose, and residualoil-containing biomass feedstock in the whole stillage. In one or moreembodiments, the secondary fermentation product can comprise at leastabout 0.1, 0.5, 1, or 2 and/or not more than 30, 25, 20, or 10 weightpercent of oil. More particularly, the secondary fermentation productcan comprise in the range of about 0.1 to 30, 0.5 to 25, 1 to 20, or 2to 10 weight percent of oil.

Moreover, in various embodiments, at least a portion of the oil in thesecondary fermentation product can be free oil. In one or moreembodiments, the secondary fermentation product can comprise at leastabout 0.1, 0.5, 1, or 2 and/or not more than 30, 25, 20, or 10 weightpercent of free oil. More particularly, the secondary fermentationproduct can comprise in the range of about 0.1 to 30, 0.5 to 25, 1 to20, or 2 to 10 weight percent of free oil.

As previously noted, the oil in the secondary fermentation product hascommercial value and, thus, it is generally desirable to remove thisbyproduct at some point from the fermentation products. Unlike the priorart processes, the processes and systems described herein are able toseparate and extract the oil in the secondary fermentation product priorto removing the ethanol from the fermentation product.

As described above, the free oil in the secondary fermentation productcan be brought to the surface of the fermentation product by introducinga gas into the fermentation product. In such embodiments, the introducedgas can cause the oil in the fermentation product to rise to the top ofthe fermentation product, thereby making it easier to recover. Thus, invarious embodiments, a gas may be introduced into the secondaryfermentation product in order to separate the fermentation product intoan oil-poor component and an oil-rich component comprising the free oil.

In one or more embodiments, the gas introduced into the secondaryfermentation product can be at least partially derived from, oralternatively, entirely derived from, the gas produced during thesecondary fermentation by the yeasts and/or a gas from the gas injectionsystem 10. The gas can comprise one or many types of gases. In variousembodiments, the gas comprises carbon dioxide, air, nitrogen, orcombinations thereof. In certain embodiments, the gas comprises carbondioxide.

In various embodiments, the gas can be introduced into the secondaryfermentation product through the use of a gas injection system 10, whichcan pump a gas stream into the bottom of the fermentation tank 44thereby allowing the introduced gas to pass through the secondaryfermentation product. The gas injection system 10 can be configured topump the gas into the fermentation tank 44 at a sufficient pressure thatcan overcome the head pressure of the fermentation tank. In certainembodiments, the gas injection system can be the same system that wasused in the primary fermentation. Alternatively, the gas injectionsystem can be different from the gas injection system utilized duringthe primary fermentation.

In various embodiments, the gas introduced into the secondaryfermentation product can be at least partially derived, oralternatively, entirely derived from the gases produced duringfermentation by the yeasts. As the yeasts ferment the sugars in thefeedstock, various gases can be produced, such as carbon dioxide. Forinstance, the secondary fermentation can produce in the range of about0.1 to 3, 0.3 to 2.5, 0.5 to 1.5, or 0.7 to 1.2 pounds of carbon dioxideper bushel of grain.

In certain embodiments, it may be difficult or impose a safety risk toremove oil from the top of an active fermenter. In these cases, it maybe reasonable to process the fermentation product through any number ofadditional steps until it is safe to remove the oil from the top oftank. These additional process steps are discussed below and caninclude, for example, distillation, pressing, and centrifugation. Thetankable liquids left after these processes can then be subjected to gasbubbling by means of the gas injection system 10 in an optional holdingtank 46 as shown in FIG. 2.

The optional holding tank 46 as shown in FIG. 2 can be used to hold thefermentation product after it has been subjected to any number ofpost-fermentation treatment steps, but prior to being separated intooil-poor and oil-rich components as described above. In variousembodiments, the secondary fermentation product can be introduced into aholding tank 46 where a gas can be introduced into the fermentationproduct, thereby separating the fermentation product into the oil-poorand oil-rich components discussed above. In such embodiments, the gascan be introduced into the holding tank 46 from the gas injection system10. It should be noted that the gas introduced into the holding tankwill generally come from the gas injection system since most of thefermentation will be finished by this point. An advantage of the gasinjection system is that the secondary fermentation product can beseparated in non-fermentation tanks

During the gas introduction steps, the gas can be introduced into thefermentation product while in the fermentation tanks 44 and/or holdingtank 46 at a sufficient rate so as to cause the fermentation product toseparate into the oil-poor and oil-rich components. In variousembodiments, the gas can be introduced into the fermentation product ata rate of at least about 1, 5, 10, 15, 20, 25, 30, 35, 40, or 45 cm³/minand/or not more than about 1,000, 750, 500, 400, 350, 300, 250, 200,150, or 100 cm3/min. More particularly, the gas can be introduced intothe fermentation product at a rate in the range of about 1 to 1,000, 5to 750, 10 to 500, 15 to 400, 20 to 350, 25 to 300, 30 to 250, 35 to200, 40 to 150, or 45 to 100cm³/min. Furthermore, the gas can beintroduced into the fermentation product over a time period of at least0.1, 0.5, 1, 2, or 3 hours and/or not more than 24, 12, 10, 8 or 6hours. More particularly, the gas can be introduced into thefermentation product over a time period in the range of 0.1 to 24 hours,0.5 to 12 hours, 1 to 10 hours, 2 to 8 hours, or 3 to 6 hours.

Furthermore, it has been observed that agitation rates within thefermentation tanks 44 and/or holding tank 46 can have an effect on theseparation of the secondary fermentation product into the oil-poor andoil-rich components during the gas introduction steps. It was observedthat holding agitation rates to a low level would allow at least aportion of the free oil to float to the top of the fermentation product.In such cases, as long as the agitation rates are not high enough tocause a downward velocity that overcomes the buoyancy of the oil, thefree oil can continue to float and be recovered. If the fermentationproduct is subjected to excessive agitation, then the free oil can beredistributed within the fermentation product as bound oil.

In many embodiments, the fermentation tanks 44 can have an agitator asdescribed above. In various embodiments, the agitation rate of theagitator during the gas introduction step can be less than 100, 50, 20,5, or 1 RPM. Furthermore, in embodiments where the gas introduction stepoccurs in the fermentation tank, the agitation speed of the agitatorduring the gas introduction can be at least 50, 75, 90, or 99 percentless than the agitation speed of the agitator during fermentation priorto the gas being introduced.

In various embodiments, the fermentation product is subjected tosubstantially no agitation or no agitation during the gas introductionstep.

It should be noted that the gas introduction step can occur duringfermentation or after fermentation when the yeasts have finishedconverting the sugars into the various fermentation products. As notedabove, the gas introduction step, and the subsequent removal of theoil-rich component, can occur in the fermentation tanks 44 or holdingtank 46.

Turning back to FIG. 2, after separating the primary fermentation intothe oil-poor and oil-rich components in the fermentation tanks 44 and/orholding tank 46, the oil-rich component can be recovered from thefermentation tanks 44 and/or the holding tank 46 using an oil recoverysystem 48. The oil recovery system 48 can comprise any system or meansknown in the art that are capable of removing the top oil-rich componentfrom the tanks such as, for example, a pumping apparatus or industrialpipette. For example, the oil recovery system could comprise a pipe andpump connected to the tank that could remove the top layer comprisingthe oil-rich component. In such embodiments, the pipe and pump couldalso remove the top 1% of the fermentation product to ensure that most,if not all, of the free oil is recovered from the fermentation tank.

The recovered oil-rich component removed by the oil recovery system 48can contain the majority of the free oil originally found in thefermentation product. For example, the recovered oil-rich component cancomprise at least about 25, 50, 75, 90, 95, or 99 percent of the freeoil originally present in the fermentation product. Furthermore, therecovered oil-rich component can comprise at least about 25, 50, 75, 85,90, 95, or 99 weight percent of oil that was derived from theoil-containing biomass feedstock used in the primary fermentationprocess. Moreover, the recovered oil-rich component may comprise an oilcontent by weight percentage that is at least 25, 50, 75, or 90 percentgreater than the oil content by weight percentage of the secondaryfermentation product.

In addition to its high oil content, the recovered oil-rich componentmay also comprise some incidental fermentation byproducts. Theseincidental fermentation byproducts can include any of the other productsproduced during fermentation such as, for example, ethanol, glycerol,acetic acid, lactic acid, and unconverted biomass feedstock. Generally,the recovered oil-rich component can comprise less than about 20, 10, 5,1, or 0.1 weight percent of incidental fermentation byproducts.Moreover, the recovered oil-rich component can comprise less than about20, 10, 5, 1, or 0.1 weight percent of water.

In various embodiments, it may be desirable to further treat therecovered oil-rich component in an oil purification system 50 as shownin FIG. 2 in order to concentrate the oil and remove the undesirablebyproducts therein. The oil purification system 50 can comprise anysystem known in the art that is capable of purifying oil such as, forexample, a filter membrane, a centrifuge, a settling tank, or acombination thereof. In one or more embodiments, the oil purificationsystem can be the same system used during the primary fermentation.Alternatively, the secondary fermentation can utilize a different oilpurification system than the primary fermentation.

The purified oil from the oil purification system 50 can comprise atleast about 50, 85, 95, 99, or 99.9 weight percent of oil. Furthermore,the purified oil can comprise less than about 5, 3, 1, 0.1, or 0.01weight percent of water. Moreover, the purified oil can comprise lessthan about 10, 5, 3, 1, or 0.1 weight percent of incidental fermentationbyproducts.

In various embodiments, the secondary fermentation can produce at leastabout 0.25, 1, 1.25, or 1.5 and/or not more than about 4, 3, 2.5, or 2pounds of recovered oil per bushel of grain. More particularly, thesecondary fermentation can produce in the range of about 0.25 to 4, 1 to3, 1.25 to 2.5, or 1.5 to 2 pounds of recovered oil per bushel of grain.Similarly, the secondary fermentation can produce at least about 0.1,0.2, 0.3, or 0.7 and/or not more than about 5, 4, 3, or 1.2 liters ofrecovered oil per bushel of grain. More particularly, the secondaryfermentation can produce in the range of about 0.1 to 5, 0.2 to 4, 0.3to 3, or 0.4 to 1 liters of recovered oil per bushel of grain.

As noted above, the incidental fermentation product removed by the oilpurification system 50 can be recycled back to the fermentation tank 44for further conversion and/or sent to the distillation column 52 forfurther processing.

As shown in FIG. 2, after recovering the oil-rich component, theoil-poor component remains in the fermentation tank 44 and/or holdingtank 46. The remaining oil-poor component generally comprises thenon-oil byproducts produced during fermentation. For example, theoil-poor component generally comprises ethanol, glycerol, acetic acid,lactic acid, unconverted biomass feedstock, and otherfermentation-derived alcohols. In one or more embodiments, the oil-poorcomponent can comprise at least about 10, 15, 20, or 25 and/or not morethan about 70, 60, 50, or 40 weight percent of ethanol. Moreparticularly, the oil-poor component can comprise in the range of about10 to 70, 15 to 60, 20 to 50, or 25 to 40 weight percent of ethanol.Furthermore, the oil-poor component comprises less than 20, 10, 5, or 1weight percent of oil. Additionally or alternatively, the oil-poorcomponent can comprise an oil content by weight percentage that is atleast 25, 50, 75, or 90 percent lower than the oil content by weightpercentage of the secondary fermentation product. In embodiments where aholding tank 46 is utilized, the remaining oil-poor component in theholding tank 46 can be sent to the fermentation tanks 44 for furtherfermentation if necessary.

Turning again to FIG. 2, the remaining oil-poor component in thefermentation tanks 44 or holding tank 46 can be transferred to one ormore distillation columns 52. In the distillation columns 52, theethanol can be removed from the oil-poor component and transferred toone or more rectifiers 54 and molecular sieves 56 to remove moisturetherefrom. The final alcohol can then be transferred to one or moreethanol holding tanks 58 where it may be denatured before use as a fuelor fuel additive.

The liquid and solid mixture that remains in the distillation columns 52after the alcohol has been removed is the secondary whole stillage. Thesecondary whole stillage generally settles to the bottom of thedistillation columns 52 and can then be transferred to one or more wholestillage holding tanks 60.

Although not shown in FIG. 2, the secondary whole stillage produced bythe secondary fermentation step can be further treated inpost-fermentation processes. These processes are discussed above inregard to the whole stillage of the primary fermentation.

The primary fermentation and secondary fermentation steps describedherein can be used to convert the majority of the starch, cellulose,and/or hemicellulose originally found in the biomass feedstock intouseful products. For example, the combined output of the primaryfermentation and the secondary fermentation can produce at least about2.65, 2.8, 2.95, or 3.1and/or not more than about 4.0, 3.7, 3.5, or 3.3gallons of ethanol per bushel of grain. More particularly, the combinedoutput of the primary fermentation and the secondary fermentation canproduce in the range of about 2.65 to 4.0, 2.8 to 3.7, 2.95 to 3.5, or3.1 to 3.3 gallons of ethanol per bushel of grain.

Furthermore, the process described herein can also improve grain oilrecovery by breaking down and fermenting the fiber in the fat-rich germportion of the grains. In prior art processes, the oil tends to becometrapped within the fiber matrix of the germ, thus making it difficult toremove. Most fermentation plants report yields of 15 to 35% of the totaloil capable of being recovered. By breaking down the fiber as describedherein, substantially all of the grain oil can be recovered. Forexample, the combined output of the primary fermentation and thesecondary fermentation can produce at least about 0.25, 1, 1.25, or 1.5and/or not more than about 5, 4, 2.5, or 2 pounds of oil per bushel ofgrain. More particularly, the combined output of the primaryfermentation and secondary fermentation can produce in the range ofabout 0.25 to 5, 1 to 4, 1.25 to 2.5, or 1.5 to 2.0 pounds of oil perbushel of grain.

Based on the above, the oil recovery processes and systems describedherein contain multiple advantages. Compared to the prior art, lessequipment and energy can be required to separate and recover the oilfrom the fermentation product. For example, the processes describedherein can remove the need for a centrifugation step and other heatingor chemical treatments commonly used in prior art processes. Thus, theinventive processes and systems can therefore save on both equipment andenergy costs.

Furthermore, by drawing the oil off during the fermentation stage asdescribed above, there is less chance of oil loss through other parts ofthe process. In the prior art processes, the distillation, decanting,and evaporation steps, along with the associated heating and pumping,can disperse the oil into microscopic droplets. Consequently, thesedroplets can be very difficult to separate, thereby making a significantportion of the oil more difficult to recover. Thus, this can greatlyreduce oil yields.

The preferred forms of the invention described above are to be used asillustration only, and should not be used in a limiting sense tointerpret the scope of the present invention. Modifications to theexemplary embodiments, set forth above, could be readily made by thoseskilled in the art without departing from the spirit of the presentinvention.

The inventors hereby state their intent to rely on the Doctrine ofEquivalents to determine and assess the reasonably fair scope of thepresent invention as it pertains to any apparatus not materiallydeparting from but outside the literal scope of the invention as setforth in the following claims.

DEFINITIONS

It should be understood that the following is not intended to be anexclusive list of defined terms. Other definitions may be provided inthe foregoing description, such as, for example, when accompanying theuse of a defined term in context.

As used herein, the terms “a,” “an,” and “the” mean one or more.

As used herein, the term “and/or,” when used in a list of two or moreitems, means that any one of the listed items can be employed by itselfor any combination of two or more of the listed items can be employed.For example, if a composition is described as containing components A,B, and/or C, the composition can contain A alone; B alone; C alone; Aand B in combination; A and C in combination, B and C in combination; orA, B, and C in combination.

As used herein, the terms “comprising,” “comprises,” and “comprise” areopen-ended transition terms used to transition from a subject recitedbefore the term to one or more elements recited after the term, wherethe element or elements listed after the transition term are notnecessarily the only elements that make up the subject.

As used herein, the terms “having,” “has,” and “have” have the sameopen-ended meaning as “comprising,” “comprises,” and “comprise” providedabove.

As used herein, the terms “including,” “include,” and “included” havethe same open-ended meaning as “comprising,” “comprises,” and “comprise”provided above.

As used herein, references to “one embodiment,” “an embodiment,” or“embodiments” mean that the feature or features being referred to areincluded in at least one embodiment of the technology. Separatereferences to “one embodiment,” “an embodiment,” or “embodiments” inthis description do not necessarily refer to the same embodiment and arealso not mutually exclusive unless so stated and/or except as will bereadily apparent to those skilled in the art from the description. Thus,the present invention can include a variety of combinations and/orintegrations of the embodiments described herein.

NUMERICAL RANGES

The present description uses numerical ranges to quantify certainparameters relating to the invention. It should be understood that whennumerical ranges are provided, such ranges are to be construed asproviding literal support for claim limitations that only recite thelower value of the range as well as claim limitations that only recitethe upper value of the range. For example, a disclosed numerical rangeof 10 to 100 provides literal support for a claim reciting “greater than10” (with no upper bounds) and a claim reciting “less than 100” (with nolower bounds).

1-11. (canceled)
 12. A method for recovering an oil from whole stillagethe method comprising: (a) fermenting a whole stillage to therebyproduce a fermentation product comprising an oil; (b) introducing a gasinto the fermentation product to thereby form an oil-poor component andan oil-rich component; and (c) separating the oil-rich component fromthe oil-poor component to thereby produce a recovered oil-rich product.13. The method of claim 12, wherein the gas is introduced into thefermentation product at a rate of 5 to 1,000 cm.sup.3/min.
 14. Themethod of claim 13, wherein at least a portion of the introducing ofstep (b) occurs during at least a portion of the fermenting of step (a15. The method of claim 14, wherein the fermenting of step (a) and theintroducing of step (b) occur in a container comprising an agitator,wherein the <agitator operates at a predetermined fermentation agitationrate during the fermenting of step (a) and a predetermined gas agitationrate during the introducing of step (b), wherein the gas agitation rateis at least 50 percent less than the fermentation agitation rate. 16.The method of claim 13, wherein the gas is introduced over a period of0.1 to 24 hours.
 17. The method of claim 12, wherein the recoveredoil-rich product comprises at least about 75 weight percent of oil 18.The method of claim 12, wherein the recovered oil-rich product comprisesat least about 50 percent of the oil originally present in thefermentation product
 19. The method of claim 12, wherein at least aportion of the gas is produced by a gas sparger, gas diffuser, aerationturbine, venturi tube, or a combination thereof. 20-26. (canceled)
 27. Asystem for recovering an oil from biomass, the system comprising: (a) afermentation tank configured to ferment an oil-containing biomassfeedstock into a fermentation product; (b) a gas injection system, influid communication with the fermentation tank, wherein the gasinjection system is configured to introduce a gas into the fermentationproduct thereby separating it into an oil-poor component and oil-richcomponent; and (c) an oil recovery system in fluid communication withthe fermentation tank, wherein the oil, recovery system is configured torecover the oil-rich component.
 28. The system of claim 27, furthercomprising an oil purification system in fluid communication with theoil recovery system, wherein the oil purification system is configuredto remove solids and non-oil components from the oil-rich component. 29.The system, of claim 27, further comprising a holding tank in fluidcommunication between the fermentation tank and the oil recovery system,wherein the holding tank is configured to hold the fermentation productfrom the fermentation tank
 30. The system of claim 29, wherein the gasinjection system is in fluid communication with the holding tank and isconfigured to introduce the gas into the holding tank.